The invention relates generally to a device for repairing vasculature, and more particularly to a design for stents that increases flexibility while still allowing the stent to be crimped to a small profile for delivery to an implant site.
Stents conventionally repair blood vessels that are diseased. Stents are generally hollow and cylindrical in shape and have terminal ends that are generally perpendicular to their longitudinal axis. In use, the conventional stent is positioned at the diseased area of a vessel and, after deployment, the stent provides an unobstructed pathway for blood flow.
Repair of vessels that are diseased can be particularly challenging since a stent used in the repair must be precisely positioned, provide adequate coverage of the disease and maintain vessel patency in order to allow adequate blood flow. Therefore, the stent must provide adequate coverage to the diseased portion of the vessel, without compromising blood flow, and extend to a point within and beyond the diseased portion. Where the stent provides coverage to the vessel at the diseased portion, yet extends into the vessel lumen at a bifurcation, for example, the diseased area is repaired, but blood flow may be compromised in other portions of the bifurcation. Unopposed stent elements may promote lumen compromise during neointimal formation and healing, producing restenosis and requiring further procedures. Moreover, by extending into the vessel lumen at a bifurcation, the stent may block access for further interventional procedures.
Recently, the art has taught the use of stents having a cylindrical body with rings aligned along a longitudinal axis, where each ring has a delivered diameter in which it is crimped or compressed tightly onto a balloon catheter or within a delivery catheter, and an implanted diameter where the stent is implanted in a vessel. Each ring includes a number of first peaks and one or more second peaks, with at least one second peak of each ring connected to a second peak of the adjacent ring by a link, the rings and links being made of struts. The first peaks are configured to spread apart to permit the rings to be expanded outwardly or to be compressed radially inwardly onto a delivery catheter. The second peaks and links provide longitudinal connection points between the rings.
By varying the number of rings and first peaks, the outward expansion of the various sections of the implanted stent can be varied and, thereby provide the required support at selected areas of the patient's lumen. Moreover, by varying the length and shapes of the links which connect the rings, the expandability, flexibility and degree of compression attainable may be customized. Flexibility of a stent is important with regard to both the ability of the stent to conform to the curvature of a tortuous artery after expansion and to the ability to maneuver the compressed stent through anatomy for delivery to the implant site. In particular, non-linear links may have undulating portions which have portions that are perpendicular to the longitudinal axis of the stent and which act as a hinge to enhance stent flexibility.
Although the undulating portions improve stent flexibility, they also may limit the extent of compression that may be achieved in the stent and therefore, result in a larger than desired delivery profile. Because the undulating portions include structure that extends generally perpendicular to the axis of the stent, in certain designs they will contact the adjacent first peaks when the stent is compressed, thereby limiting the degree of compression achievable. Additionally, the undulating portions may only accommodate small deformations that occur during stent delivery. Thus, the undulating portions may do little to accommodate large deformations occurring inside the vessel after the stent is expanded. Moreover, the undulating portions typically improve flexibility only in a longitudinal direction, but not in planes or directions perpendicular to the longitudinal axis of the stent.
Accordingly, what is needed is a stent with structure providing the stent with both desired flexibility and delivery profile. The present invention is directed to this need.